High-order Harmonic Components Research Articles

Hydrodynamics investigation of a three-dimensional fish swimming in oblique flows by a ghost cell method

Fish in nature can encounter various flow environments. This paper numerically simulated a 3D (three-dimensional) carangiform fish swimming in oblique flow. The numerical model adopts a robust ghost cell method with graphics processing unit acceleration. The dynamic performance and the 3D wake evolutions are discussed under different Strouhal numbers and attack angles. It is found that the thrust along the swimming direction would get enhanced with more energy consumption as the Strouhal number (St) rises. The attack angle can get the similar but less significant effect. Also, the stall angle of θ = 40° is approximately determined, which is independent of the Strouhal number. However, the flexible deformation can reduce the adverse effects of the stall. In terms of the wake structures, they are transitioned from the two rows of vortex streets at St = 0.2 to the three rows at St = 0.6, and even to the four rows at St = 1. The connected oblique vortex ring rows induced by the undulating caudal fin contributes to the thrust and lateral forces dominantly. As the St rises, the vortex ring rows is transformed from the typical von Karman vortex streets to the reverse one, indicating the generation of thrust. The slender, parallel vortex contrails are caused by the detachment of leading-edge vortices (LEVs), and they induce the high-order harmonic components in force coefficients. The oblique angle of the vortex rings grows with the Strouhal number, while it is hardly affected by the attack angle. As the attack angle grows, the wake is turned from the disconnected hairpin vortices to the intertwined vortex rings and losses the spanwise symmetry. Moreover, the reattachment of the LEV is not observed after the stall angle.

Comparison between linear and quadratic power take off for a single chamber land-fixed oscillating water column (OWC)

This study examines the influence of turbine response type on the performance of a land-fixed Oscillating Water Column (OWC) under second-order Stokes waves of varying heights. Numerical modelling techniques, including the Finite Element Method, incompressible Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear-Stress Transport (SST) k-ω turbulence model, and an Arbitrary Lagrangian–Eulerian (ALE) scheme, were employed to gain insights into OWC behaviour. The linear turbine consistently displayed reduced efficiency with increasing wave height, maintaining a stable peak non-dimensional wave number (kh). Conversely, the quadratic turbine exhibited peak efficiency within a narrower wave height range, strongly influenced by wave height. Non-dimensional volume flow rate, non-dimensional chamber pressure, chamber volume, and maximum force on the front wall remained unaffected by changes in wave height for the linear turbine. In contrast, the quadratic turbine was notably impacted by variations in wave height. Moreover, the quadratic turbine revealed stronger odd-numbered higher-order harmonic components in both force and pressure due to its non-linear response. Notably, both linear and quadratic response types exhibited sloshing at similar wave numbers, suggesting minimal influence of turbine response on sloshing behaviour. Finally, the derived non-dimensional turbine coefficients proved both turbines could scale OWC models with negligible scaling effects from the turbine.

Physical reservoir application of random network of gold nanoparticles fabricated by multi-step immersion in gold colloidal solution

We fabricated a random network of gold nanoparticles (RN-GNPs) over 12 NiCr/Au electrodes by using a multi-step immersion method, where a sample was immersed in a gold colloid solution three times. Nonlinear current–voltage characteristics due to the Coulomb blockade were observed at 77 K. For demonstration of physical reservoir applications, input–output characteristics of the RN-GNPs were also measured in a one-input, nine-output terminal configuration. Distorted output voltage waveforms were obtained for a sinusoidal voltage input of 100 Hz. The higher-order harmonic components were confirmed in the frequency spectra of the outputs. The waveform reconstruction task and short-term storage capacity estimation were performed by an echo state network model with ridge regression and linear regression, respectively.

Trajectory optimization method based on ellipse model for dynamic motion control of piezoelectric transducer in an optical resonance cavity

External-cavity diode laser (ECDL) can continuously change the output wavelength by scanning its optical resonance cavity (ORC), which is a piezoelectric transducer (PZT) actuated mechanical system. However, because of the inherent hysteresis characteristic of PZT and limited system bandwidth, the dynamic response of the ORC system exhibits both the nonlinearity and vibration while high-frequency triangular wave scanning, thereby resulting in the degradation of the output wavelength performance of the ECDL. As a result, a trajectory optimization method is presented to improve the scanning characteristics of the ORC system. Firstly, the hysteresis behavior of PZT is described by the elliptic model to generate a compensation voltage for the PZT. Secondly, the cusp region of the compensation voltage is optimized by a frequency domain objective function to greatly reduce the high-order harmonic components of the compensation voltage. Finally, an optimal voltage trajectory for driving the ORC system is obtained. The experimental results demonstrate the validity of our proposed trajectory optimization method for simultaneously suppressing the nonlinearity and vibration of the ORC system within the scanning frequency of 100 Hz.

The nonlinearity of scattering waves due to interaction between focusing waves and floating production storage and offloading

The study of the full-scale wave–structure interaction is essential to our understanding of the nonlinear characteristics of offshore structures in real-sea states. This paper deals with full-scale numerical studies of the interactions between focusing waves and a fixed floating production storage and offloading (FPSO) in an efficient potential-viscous coupled method. The potential-viscous method combines in-house computational fluid dynamics code developed at Shanghai Jiao Tong University (SJTU) for naval architecture and ocean engineering (naoe) based on an open field operation and manipulation (FOAM), i.e., naoe-FOAM-SJTU solver, with high-order spectral method. The approach is verified on a model-scaled case and shows reasonably good agreement with experimental data. A phase-separation method and a dynamic mode decomposition method are utilized to extract linear and higher-order harmonic components from the scattering waves. The scattering waves around the FPSO are found to affect the higher-order harmonic components. Two kinds of scale ratios are considered to magnify the focusing wave and FPSO by 10 and 100 times to discuss the scale effect, both non-breaking and green water conditions are included to investigate the flow phenomenon. The harmonic components of scattering waves are not proportional to the scale ratio, and the scale effects influence more on higher-order harmonic components. The third- and fourth-order harmonic components of scattering waves around the FPSO in large-scale cases are obvious.

Experimental investigation on wave-induced bending moments of a 6,750-TEU containership in oblique waves

This study aims at the experimental investigation of wave-induced motions and loads of a containership model without forward speed in -120 degree oblique regular waves to study the influence of the wave steepness and provide reference data for future benchmark studies. A mooring system with 4 horizontally arranged spring lines was used to maintain the heading angle of a 1/65 scaled 9-segmented model designed to be as rigid as possible.Focuses were on studying the nonlinear effects due to the wave steepness on the vertical bending moment (VBM) and horizontal bending moment (HBM) near amidships, and 6-DOF motions at the center of gravity (COG) of the model. Several wave series that are distinguished by wave steepness were considered in the experiment accordingly. Each series consists of waves with various periods that were intended to cover the peak of the wave bending moment transfer functions. Through this, the nonlinear wave effects on the responses of the rigid body at various periods were determined. It was confirmed that the steeper wave contributes to the increase in the higher-order harmonic components including slamming events in the bending moments measured. The change in the characteristics of the wave bending moments according to the change in wave steepness was found to be very different from the linear response.A detailed discussion was made on the influence of the mooring system on the asymmetric horizontal bending moment (HBM) and the change in the average yaw motion. Experiments with and without a mooring system under the same wave condition were conducted, and the effect of the mooring system was identified. It was qualitatively confirmed that the mooring system’s restoring moment correlates with the asymmetric HBM and average yaw movement change.

A Dual-Frequency-Detuning Method for Improving the Coupling Tolerance of Wireless Power Transfer

This letter proposes a dual-frequency-detuning method for wireless power transfer systems to gain a smooth power profile in large coupling variation ranges. The application of the detuning method in the dual-frequency resonant network is explored to adjust the equivalent impedance of each frequency channel at different coupling conditions. Accordingly, the proposed method can freely regulate the voltage gain and output power curves even under a square-wave voltage excitation with high-order harmonic components. By designing the system properly, both the fundamental and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> frequency channels alternately serve as the main power transfer channel under strong and weak coupling conditions, so less power fluctuation over a large coupling variation is realized. A 130W prototype is developed, and the experimental results show that the maximum power fluctuation is less than 6.8% against coupling coefficient variations from 0.35 to 0.74.

Enhanced performance of hysteresis controlled single phase Ac/Dc buck converter system using cubic boron arsenide semiconductor material

This paper presents a single phase AC-DC buck converter using Hysteresis controller in order to provide superior response. As an alternative to the DC grid, the single phase AC/DC buck converter is getting prominence. The rectifier's AC output is fed into a Buck converter (BC) and then filtered with a filter. Higher order harmonic components are present in the power drawn by nonlinearandunbalancedloads,whichinturn raises the supply current’s totalharmonicdistortionlevel. In comparison to other controllers, hysteresis current controllers are well known for their robustness, faster error tracking, greater dynamic response and simplicity of implementation. In this study, a single phase buck converter system with a Proportional Integral controller (PIC) and a Hysteresis controller is modelled and simulated (HC). The findings of comparing the performance of buck converters with PIC and HC are presented. The outcomes show that an HC controlled Buck Converter responds more quickly. Because of improvements in material science and a desire for higher performance, wide band-gap semiconductors are used in switching circuits. This paper also discusses the cubic boron arsenide semiconductor material, which is used to create the power electronic switches used in AC-DC converters and has good thermal conductivity and high manoeuvrability for electrons and holes.

Modal analysis of the influence of freestream on global rotor noise

The exact frequency domain solutions of the noise for rotating point sources are extended to acoustic modal domain. Moreover, the modal analysis method from the aerodynamic loading in the source modal domain to the aeroacoustic noise in the acoustic modal domain is established. A large amount of work has been done to directly predict the rotor noise at the observation points. However, there is very little work to consider the acoustic characteristics of the rotor contained in a large amount of data, such as the evolution of global noise in the space. In this study, the modal analysis method is used to quantify the acoustic characteristics of the rotor under different flight conditions. It is concluded that the acoustic modal components of the noise from the in-plane sources (mass source, radial force and circumferential force) are similar, but they are cross distributed with that from the out-of-plane source (axial force). The out-of-plane source becomes the main contribution source with the increase of forward speed, owning to the high radiation capacity of high-order harmonic components.

Active Compensation-Based Harmonic Reduction Technique to Mitigate Power Quality Impacts of EV Charging Systems

This article presents a novel active compensation-based harmonic reduction (ACHR) technique in order to mitigate the existing third harmonic component in the input current of the power factor corrector (PFC) circuit in electric vehicle (EV) charging systems. Traditional PFC control scheme includes an outer voltage loop to control the output dc voltage and an inner current loop to ensure that the grid current is sinusoidal. The work shows how third and other high-order harmonic components are created, while the signal is transmitting through the voltage control loop, and then, an analytical model is developed to calculate the dominant third harmonic magnitude according to the circuit specifications and control parameters. The ACHR approach takes advantage of multilevel filter design to prevent the presence of high-order odd harmonics in addition to mitigating the existing third harmonic component created by the voltage control loop before it is passed through the current control loop. ACHR is designed optimally, and its performance is analyzed in detail to have a robust and stable closed-loop system while keeping the characteristics of fundamental harmonic. A totem-pole boost PFC proof-of-concept is built to verify the proposed ACHR technique. The results show that the third harmonic magnitude is reduced from 244 mA in conventional control scheme to 130 mA in the proposed ACHR technique. Moreover, total harmonic distortion (THD) in input current is decreased from 4.88% to 4.03%.

Harmonic Detection Method Based on Particle Swarm Optimization and Simulated Annealing Algorithm of Electrohydraulic Servo System

Due to the comprehensive influence of many nonlinear coupling factors within a system, when the input signal provided by an electrohydraulic servo shaker is sinusoidal, it often leads to the existence of high-order harmonic components of the system, which makes the output servo signal parameters exist extremely serious. Therefore, the detection of harmonics of the electrohydraulic servo shaker has very important application significance. In this paper, by using simulated annealing (SA) based harmonic detection, a kernel function is introduced to study area influence-based particle swarm optimization (PSO). Using a super accurate and fast global convergence brought by the combination of hybrid particle swarm optimization algorithm and simulated annealing algorithm, it can quickly jump out of the trap of traditional local optimization algorithms and a more stable, high-precision, as well as fast global convergence optimal solution can be obtained. Through the detection and simulation of the amplitude and phase of the harmonics in the system, by comparing the PSO-SA detection with PSO detection, it is proved that the PSO-SA algorithm can well satisfy the accuracy of the detection system, which has advantages such as a fast convergence speed, a high search accuracy, etc.; meanwhile, it is simple and easy to implement.

Stability Assessment of Modular Multilevel Converters Based on Linear Time-Periodic Theory: Time-Domain vs. Frequency-Domain

The periodic characteristic of modular multilevel converter (MMC), which originates from the multi-harmonic couplings among internal dynamics, results in challenges to develop the linear time-invariant (LTI) model of MMC. The linearization of MMC is inherently around time-periodic equilibrium trajectory. In this paper, two different methods to assess small-signal stability of MMC are compared. Both are based on the linear time-periodic (LTP) systems theory, but one is in the time domain (TD) and the other is in the frequency domain (FD). The LTP model of MMC is derived from the linearized arm averaged model. Then, an LTI model for the LTP system is constructed in the FD through the harmonic state-space method. Small-signal stability analysis based on Floquet theory and generalized Nyquist criterion, that accompany TD and FD, are introduced and compared. It is demonstrated that models developed in both domains can effectively capture the small-signal behavior of MMC. Third and higher-order harmonic components of the states have significant effect on the impedance-based stability analysis of MMC around mid-frequency range. Analytical results are validated by electromagnetic transient simulations based on the MMC aggregated model.

Power Quality Problems Due to Transformer Inrush Current

Transformer energization can produce a large nonsinuoidal inrush current which contains both odd and higher order harmonic components that can put transformer winding under mechanical stress. Additionally, they can cause irregular tripping of harmonic protection relays. Furthermore, in relatively weak power systems, such as is the Bosnian system, the superposition of harmonic components with system resonance frequencies may produce temporary overvoltages (TOV). Transformer winding failures and metal oxide surge arrester (MOA) energy stresses can occur due to TOV. The paper demonstrates a case study of an energization of a 220/110 kV transformer and power quality problems that can appear due to higher harmonics. Energy stresses of MOA provoked by transformer energization are considered in the paper.

In-Place Evaluation of Powering and Signaling Within Fan-Out Multiple IC Chip Packaging

This article confirms the advantage of fan-out (FO) packaging in the electrical performance of power delivery among integrated circuit (IC) chips with the best use of land side capacitors (LSCs). On-chip in-place waveform measurements quantitatively evaluate the integrity of powering and signaling within FO wafer level packaging (FOWLP) multiple chip module (MCM) demonstrators, where a pair of IC chips are assembled with LSCs with different sizes and structures. The IC chip incorporates an array of 12 digital cores and on-chip waveform monitor (OCM) circuits. Each digital core consists of a low-voltage differential signaling (LVDS) transceiver channel that is backed by a static random access memory (SRAM)-based built-in self test (BIST) module and supplied by an on-chip voltage regulator module (VRM). The LSCs are placed on the bottom side of an FO interposer and inserted between the output of VRM and the ground plane almost ideally with the shortest length of physical traces. A Si membrane capacitor of 10 nF sustains the lowest power line impedance over the frequency range of 2.0 GHz more constantly than a multilayer ceramic counterpart, and attenuates the high-order harmonic frequency components to the clocking frequency at 750 MHz. The leverage of LSCs in powering also improves signaling and helps achieve the wider eye openings in LVDS channels. The implications are elaborated for the capacitor selections with respect to the physical types of capacitors, the size of capacitances, and the level of shares in power delivery among digital cores, all toward the higher level of integrity in powering and signaling in FOWLP MCMs.

Direct numerical simulation of interaction between a stationary crossflow instability and forward-facing steps

The interaction between forward-facing steps of several heights and a pre-existing critical stationary crossflow instability of a swept-wing boundary layer is analysed. Direct numerical simulations (DNS) are performed of the incompressible three-dimensional laminar base flow and the stationary distorted flow that arise from the interaction between an imposed primary stationary crossflow perturbation and the steps. These DNS are complemented with solutions of the linear and the nonlinear parabolised stability equations, used towards identifying the influence of linearity and non-parallelism near the step. A fully stationary solution of the Navier–Stokes equations is enforced numerically, in order to isolate the mechanisms pertaining to the interaction of the stationary disturbance with the step. Results provide insight into the salient modifications of the base laminar boundary layer due to the step, and the response of the incoming crossflow instability to these changes. The fundamental spanwise Fourier mode of the disturbance field gradually lifts up as it approaches the step and passes over it. The flow environment around the step is characterised by a sudden spanwise modulation of the base-flow streamlines. Additional stationary perturbation structures are induced at the step, which manifest in the form of spanwise-aligned velocity streaks near the wall. Shortly downstream of the step, the fundamental component of the crossflow perturbation maintains a rather constant amplification for the smallest steps studied. For the largest step, however, the fundamental crossflow perturbation is stabilised significantly shortly downstream of the largest step. This surprising result is ascribed to a modulation of the kinetic energy transfer between the base flow and the fundamental perturbation field, which is brought forward as a new step interaction mechanism. Possible non-modal growth effects at the step are discussed. Furthermore, the results from DNS indicate significant amplification of the high-order harmonic crossflow components downstream of the step.

Aerodynamic Nonlinear Energy Evolution Characteristics of Vertical Vortex-Induced Vibration of Open Bridge Girder

Compared with traditional streamlined box girders, girders with a typical open section have a highly bluff aerodynamic shape and are prone to cause vortex-induced vibration (VIV), which will affect the safety and serviceability of a bridge. In this study, the surface pressure distribution and aerodynamic nonlinearity characteristics of a typical open section are studied through wind tunnel tests and numerical simulations. Based on the synchronous measurement technology, the evolution characteristics of the surface pressure distribution in different periods of the VIV lock-in region are analyzed, and the numerical simulation of the section was performed by a user-defined function (UDF) program. The numerical simulation results are in good agreement with the wind tunnel test results. Furthermore, the multi-order components of aerodynamic force in the VIV process were decomposed by the Hilbert vibration decomposition (HVD) method. Our study found that the average pressure of the open section’s surface at the leading edge was negative, as this is where the air flow is separated. At the extreme point of the VIV lock-in region, the fluctuating pressure changes most drastically in the region ([Formula: see text]), indicating that the intensity of vortex shedding is the greatest in this region. High-order components of the aerodynamic forces acting on an open section girder can be identified by analysis. The aerodynamic damping of the open section girder is significantly reduced in the VIV lock-in region, and reaches its minimum near the extreme point of VIV. Due to the presence of high-order harmonic components, the degree of aerodynamic nonlinearity continues to increase. Moreover, the work performed by each aerodynamic component throughout the whole vibration period has different characteristics, and the influence of the third-order and above components on the VIV system can be ignored. This study can help us to further understand the aerodynamic nonlinear energy evolution characteristics of the open section, and further improve people’s understanding of the VIV system.

Performance analysis of a geometrically nonlinear isolation system subjected to high levels of excitation

This study develops a modified harmonic balance method (HBM) and uses it to analyze the vibration isolation performance of a geometrically nonlinear isolation system subjected to high levels of excitation. The modified 5th-order Taylor series expansion (TSE) is applied to simplify the geometrically nonlinear stiffness (GNS) and geometrically nonlinear damping (GND). Using a modified elliptic harmonic balance method (EHBM), we can calculate the approximate free vibration frequencies consistent with the exact solutions. After illustrating the limitation of the high-order solution assumed by Jacobi elliptic functions, a modified HBM is proposed to solve the damped cubic-quintic Duffing (CQD) equation with high-level external excitation. The stability analysis is obtained, and the characteristics of unstable regions are shown according to different values of the damping coefficient. The results show that GNS and GND profoundly affect the high-order harmonic components of amplitude-frequency response and force transmissibility. The characteristics of low frequency and resonance regimes with or without quasi-zero stiffness (QZS) are different as the amplitude of excitation increases. The modified TSE and HBM are desirable and straightforward for the detailed study of the characteristics of the GNS and GND vibration isolation system.

Monte Carlo Simulation of Random Waves at Finite Depth Based on the Joint Distribution of Wave Amplitude and its Associated Period in Nonlinear Random Waves of Finite Bandwidth

This study aims to develop a new methodology to generate random waves from a joint distribution of wave amplitude and its associated period. In doing so, the wave spectrum was derived from the joint distribution of wave amplitude and associated period and compared with the Wallops spectrum, which has been most frequently referred to in the literature. Numerical simulation shows that the nonlinearity of random waves makes a significant difference in the wave spectrum. These differences are summarized by a somewhat excessive peak period of the semi-empirical wave spectrum and underestimating wave energy over the high-frequency band. These behavioral characteristics of wave spectrum derived from the joint distribution of wave amplitude and its associated period are conceived to be due to the intrinsic property of the nonlinear random waves. The rationale of this reasoning can be found in the fact that non-negligible amount of wave energy shifts to the relatively short and long period band due to the resonant wave-wave interaction as nonlinearity is getting more pronounced as widely known in the coastal engineering community after studies of Hasselmann(1967) and Phillips(1980) on the developments of wind waves. Among the differences mentioned above, an excessively high peak period can be fully predicted by recalling that the wave period is getting shortened due to the phase difference between the free mode waves among the higher-order harmonic components appearing in random waves due to resonant wave-wave interaction and the resulting destructive interaction.

Study on Aerodynamic Nonlinear Characteristics of Semiclosed Box Deck Based on Variation of Motion Parameters

In order to study the nonlinear characteristics of self-excited aerodynamic forces of bluff body bridge section with the change of motion parameters, a numerical wind tunnel is established by the dynamic mesh technique of computational fluid dynamics (CFD). A state-by-state forced vibration method is used to identify the self-excited aerodynamic forces of single degree-of-freedom (DOF) heaving and pitching motion. Fast Fourier transform (FFT) is adopted to obtain frequency-domain data for analysis. The reliability of the obtained aerodynamic results is verified by wind tunnel tests. The results show that the high-order harmonic components are found in the self-excited aerodynamic forces of semiclosed box deck section, which are more significant in aerodynamic lift than in aerodynamic moment. The proportion of aerodynamic nonlinear components increases with amplitude. The effect of amplitude on the nonlinear components of heaving motion is generally higher than that of pitching motion, and aerodynamic moment is highly sensitive to the increase of vertical amplitude. The variation of the nonlinear components of the deck section with frequency is not a simple monotonic relationship, and there is a stationary point at 10 Hz frequency. The existence of wind attack angle makes the proportion of nonlinear components reach more than 30% and greatly increases the proportion of second harmonic. In addition, the high-order harmonic components, which are not integer multiples, are found at large amplitude and positive angle of attack.

Arm-Current-Sensorless Circulating Current Control of MMC

The circulating current and the large energy storage requirement are the two major limitations of the modular multilevel converter (MMC). The circulating current in MMC is majorly, in addition to the dc current, second harmonic in nature. If not controlled properly, it results in reduced efficiency and/or increased energy storage requirement (ESR). To enhance the efficiency, the second and the higher-order harmonic components in the circulating current of MMC are required to be suppressed. On the other hand, controlling the circulating current to have predefined magnitude and phase-angle can reduce the ESR. There are many control methods available in literature to suppress and also, to control the second harmonic circulating current (SHCC). These methods are mainly based on sensing the arm current and calculating the SHCC and then suppressing or controlling it based on the set objectives. In this paper, two control schemes are proposed to suppress the SHCC and to reduce the ESR. The proposed schemes are based on utilizing the instantaneous voltage signals of the sub-module capacitors in MMC. Hence, the sensing and communicating the sensed signal of arm currents can be avoided using the proposed schemes, which increases the reliability and leads to reduced cost and complexity. The efficacy of the proposed control schemes is verified using the simulation studies and also by using the scaled-down lab prototype of a 3-phase 7-level MMC.